Farmer Rudi Mussi and his grandson Lorenzo stand near Mussi’s almond orchard in the Sacramento-San Joaquin Delta near Stockton, Calif. The impact of a plan from Gov. Jerry Brown — to divert water from the Sacramento River to Southern California via underground tunnels — on the San Francisco Bay remains unknown thus far. (Rich Pedroncelli/AP)

Sometimes politicians are stubborn. And sometimes that stubbornness makes them continue to push projects that no longer make much sense. Consider Gov. Jerry Brown’s plan to build two massive tunnels to send even more water more reliably from the Sacramento River to farms and thirsty Southern California.

Brown’s $17 billion plan will pull up to 9,000 cubic feet per second of water from the river — just before it reaches the Sacramento-San Joaquin Delta — and divert it into two new underground tunnels, each 40 feet wide, that will eventually join with the existing state aqueducts near Tracy.

The delta tunnels will complete the state water system envisioned in the 1960s by Gov. Pat Brown, Jerry’s father. In 1982, then-Gov. Jerry Brown pushed a “peripheral canal” to bypass the Delta and send water south, but it was rejected by voters.

No one knows what impact the new tunnels will have on the San Francisco Bay. That’s not discussed in the plan’s environmental review documents. Scientists don’t even know how much water and sediment flowing from the Sacramento River to the sea is needed to maintain a healthy Bay.

What we do know is the amount of water entering the Bay has decreased by about one-third from historical levels because existing pumps send water south. This has led to decreases in fish and wildlife populations and a decline in Bay water quality. The drought has further cut river flow. Environmental researchers worry the added flow reductions from the new tunnels could further degrade the health of the Bay, leading to toxic algae blooms and an essentially dead Bay.

The flow of fresh water also keeps salt water from the ocean and Bay from traveling upstream to the Delta. However, as current pumping and drought have reduced the flow, salt water has intruded farther into the Delta, threatening its ecosystem and farms. The added diversion into the new tunnels will only make this intrusion worse.

The two tunnels are massive and could, if operated at full capacity (15,000 cfs), draw the entire flow out of the river during the late summer and fall months. The plans call for using at most 60 percent of the capacity, but the potential is there to pull more.

The tunnels don’t add one drop of water to the state’s water systems. Fixing leaks in the state’s water distribution systems — both in cities and rural aqueducts — could add enough water to the state system to supply Los Angeles for a year.

We may not need the tunnels at all.

Various state agencies will hold hearings about the plan this spring. Supervisor Scott Wiener and State Sen. Lois Wolk, whose district includes Davis and Vallejo, are trying to ensure one of those hearings will be in San Francisco.

But the tunnels plan does not need the approval of the legislature or a vote of the public. The Governor only has to get the appropriate permits from the state and the federal government and he can begin construction.

Gov. Brown expects the water agencies that will benefit from the tunnels to pay for their construction. That means ratepayers. The Santa Clara Valley Water District is the only Bay Area beneficiary of the tunnels. Proposition 13 allows some water districts to raise property taxes — without a vote of the people affected — to fund infrastructure expenses, like cost overruns.

Criticism of the tunnels project is increasing. Even the water agencies that stand to benefit from it are no longer as supportive as they once were. Yet Gov. Brown pushes ahead.

Jerry Meral, a former deputy secretary of the state’s Natural Resources Agency who supports the tunnels, once said of opponents, “I’m sure there were people who didn’t like the pyramids, but in the end they got built because, frankly, the people who had the power to build them built them.”

Meral’s analogy may be more apt than he realized. After all, the pyramids were massive infrastructure projects that really only immortalized one person.